One of the problem areas in modern day basketball is the abuse to which a basketball rim and backboard may be subjected when a player executes a "dunk" shot. In some instances, when the player has completed the dunk shot and is falling toward the ground, the player will grab the rim to retain his balance or possibly break the fall. Also, it sometimes happens that the player will subject the rim to impact loads in the execution in the dump shot by slamming his arms downwardly against the rim as he is thrusting the ball through the hoop.
Unless otherwise alleviated, the forces exerted on the rim by the various executions of the dunk shot can cause the rim to deform, or more seriously, cause the glass backboard to shatter. In either case, the problem is both expensive to correct and causes unacceptable delay of the game. For this reason, various release devices have been adopted in recent years which permit the rim to "break away" from the backboard, rather than receiving the full brunt of the impact forces. Typically, these systems have taken the approach of mounting the rim to the backboard by means of a spring mount that urges the rim towards its horizontal plane position: When a downward force is exerted on the rim sufficient to overcome the forces of the spring, the spring deflects downwardly. Then, when the downward force is released (e.g., by the player releasing the rim from his grip), the spring returns the rim to its plane position. The mechanism may also be provided with means for dampening the return motion.
A number of "breakaway" rims which employ this basic principle are known in the prior art. Examples include those shown in the following U.S. Pat. Nos. 4,111,420 (Tyner '420); 4,194,734 (Tyner '734), 4,365,802 (Ehrat); 4,433,839 (Simonseth); 4,534,556 (Estlund et al.). Although these various designs differ in some aspects (some of which will be discussed in greater detail below), they share the common characteristic that the pivoting motion which follows release of the rim is for the most part confined to a single arc of rotation, which in large part leads to the problems which have been solved by the present invention.
To illustrate this, reference is made to FIGS. 1-2, which show a "generic" breakaway rim assembly 10 of the type which is common in the prior art. As can be seen, the typical prior art assembly 10 comprises a base plate 14 and a releasable rim member 16. The base plate is a flat, generally rectangular metallic piece which is fixedly secured to the backboard 12 by means of bolts 18 at the corners of the baseplate. Extending a short distance forwardly from the upper edge of the baseplate is a short overhanging flange 20. The rim member 16 comprises a circular hoop 22 and a mounting bracket 24 that supports the hoop. This bracket 24 comprises a horizontal flange 26 which is fixedly connected to the rearward edge of the hoop 22, and a vertical flange 28 which extends downwardly from the rearward edge of the horizontal flange. A pair of support arms 30 are connected to side portions of the hoop, and extend downwardly to the lower part of the vertical flange 28.
The lower edge portion of the mounting bracket 24 is pivotally mounted to the baseplate 14 by a hinge mechanism 32. In the particular arrangement which is shown, the hinge mechanism comprises a mounting arm 34 which is welded to the vertical flange 28 and has a pair of rearwardly extending ears 36 which receive hinge pin 38. Pin 38, in turn, is received in a sleeve 40 which is welded to the baseplate 14.
The release mechanism is generally designated 42 and comprises a releasable bayonet mechanism 44 and the shock-absorbing spring mechanism 46. As can be seen more clearly in FIG. 2, the shock absorbing spring mechanism comprises a stud member 48 around which is mounted a coil spring 50. The rearward end of the stud member extends through a bore in the vertical flange 28 and is mounted to a horizontally extending bolt 52 which permits a limited up and down swinging movement of the stud member. The forward end of the stud member is provided with a retaining head 54. The coil spring 50 is retained between this and the vertical flange 28 so as to urge the rim 16 towards its normal, horizontal position.
In normal play, the rim assembly 10 is in the position which is shown in FIG. 1. Then, when a downward force of sufficient magnitude is exerted on the hoop 22, the bayonet mechanism 44 releases and the hoop pivots downwardly around the axis provided by pivot pin 38, toward the position shown in FIG. 2. As this is done, the coil spring 50 is compressed between the retaining head 54 and flange 28, so when the hoop 22 is subsequently released from the downward force, the spring causes the rim to return to its horizontal plane position, as indicated by arrow 55.
While, as has been noted above, breakaway rim mechanisms of this general type have proven to be effective in reducing the impact loads on the rim assembly, hinge mechanism 32 gives rise to certain deficiencies in use. Firstly, because the rim assembly is able to pivot downwardly only in a single arc, about the horizontally extending axis which is provided by pivot pin 38, the system is incapable of absorbing torsional loads, which are then transmitted directly to the backboard mounts. For example, an off-center downward force received at one of the lateral edges of the hoop, as indicated by arrow 56 causes torque loads which are transmitted to the backboard 12 via the mounting ears 32 at the ends of the pivot pin 38 and bolts 18, in the direction indicated by arrow 58. These rotational loads, applied at the mounting bolt holes, have been sufficient to cause the heavy glass backboard to shatter during play.
A second deficiency, in addition to and compounding the torsional problem described above, is that the amount of downward force required to cause release of the rim mechanism varies from point to point along the circular hoop. For example, a downward force F.sub.1 applied at point 60 along the forwardmost edge of the circular hoop will have the mechanical advantage which is offered by the relatively long lever arm between this point and the pivot pin 38, to effect release of the bayonet mechanism 44 and compression of the coil spring 50. However, for an impact received along the side edge of the hoop, for example at the offset point 62, the effective length of the lever arm is much shorter. As a result, a much greater downward force F.sub.2 is required to effect the same motion of the release/pivot mechanism. In other words, an impact on a side edge of the hoop requires a much greater downward force before the rim will release than an impact at its forwardmost edge. As a result, not only do the side edge impacts result in greater--and possibly excessive--loading in the frontal plane, but their increased magnitude also aggravates the torsional effect described above.
In addition to damage to the backboard and mounts, another result of this combination of factors is that prior art breakaway rims have been unable to provide entirely satisfactory performance for use in professional play. For example, the resistance of the rim before it breaks away, i.e., its "stiffness" (which is typically measured at the forward edge of the hoop) must be of a certain minimum value to meet NBA standards; if the rim is sufficiently "stiff", however, the excessively high loads and possible backboard breakage may result from side impacts. On the other hand, if the mechanism is made sufficiently "soft" to avoid the excess loading problem, then the rim will become excessively "spongy", absorbing too much energy when it is struck by a basketball during the ordinary course of play.
Although some prior designs have been configured to permit a limited degree of side-to-side motion (e.g., see the Ehrat and Tyner '734 patents), these have provided only rudimentary, limited response to side impacts, and have not addressed the root causes of the problems noted above. For example, the Tyner '734 patent shows a mounting plate having a slot 79 which permits a limited amount of deflection to the right or left, in addition to frontal plane pivoting about pin 22'. The design uses a friction structure (nut 67 and washer 68) to provide a predetermined amount of preload in the side deflection mechanism, however no provision is made for establishing a constant release force for impact anywhere along the circular hoop, and, furthermore, the apparatus employs a complicated spring/hydraulic shock absorber mechanism.
The Ehrat design, in turn, employs a ball and socket mechanism 27 located well below the plane of the hoop to permit a small degree of side-to-side motion; again, there is no equalization of the release force at various points along the rim, and also the bottom socket mechanism and its mounting bracket are flimsy and unstable, and subject to damage from vertical forces thinning from downward impacts.
Additionally, known rim assemblies employ fasteners referred to as "ram's horn" fasteners to attach the basketball net to the rim. These ram's horn fasteners are a single piece of rigid wire bent into the general shape of a ram's horn having a center loop and two end portions. The end portions are normally welded to the underside of the rim, while a loop of the basketball net is placed around, and held by, the center loop. These ram's horn fasteners pose a safety hazard to players whose hands are near the basketball rim. Specifically, the tip of a jumping player's finger may become jammed between the center loop in either of the two end portions of the ram's horn fastener, resulting in injury to the player when he begins to return to the ground. This problem is especially acute along the front portion of the rim.
Accordingly, there has existed a need for a "breakaway" basketball rim which will release in response to an impact at any point along the front or side portions of the hoop, and which will obviate the possibility of excessive torsional loads being transmitted to the backboard. Moreover, there exists a need for such a rim mechanism which will release in response to an equal downward impact force, and no matter where this is applied along the front and side portion of the hoop. Still further, there exists a need for such a rim which provides a very stable hoop for proper action when it is struck by a basketball, and which is sturdy and exhibits good wear characteristics for a long service life.